ST Regulator

[NoSpark]

It doesn't drop much with a light load. I'm going to order a couple of rectifiers, something I was going to do a year ago for spares. Another thing I observed is the frequency goes as high as 180hz after a few seconds when I use my DVOM, but holds a steady 60hz when I check the grid. I suppose another indication of a bad rectifier. The more I think about it the more I realize that the voltage has been slowly climbing.

[Ronmar]

Yep, you can get some weird stuff if you try to excite with AC.  That DVOM freq reading is an indication that something else besides the AC sinewave is present on your output.  An O-scope might shed some light on what it is, but since the system is so simple, a rectifyer problem makes perfect sense.

[BruceM]

Nospark, Soldering crimped connections in a high vibration situation is now considered bad practice. Wire failures near the solder joints due to copper embrittlement are common.  There is also a big stress riser right at the solder.

This goes against the grain for many of us old school types, but I've seen it published and seen the failures myself enough to believe it.

Best Wishes,
Bruce

[NoSpark]

Bruce, I 100% agree with you on that. I wasn't crazy about the crimps so I applied a little solder to the terminal end trying not to let the solder wick into the wire side and make it brittle. I was wondering when I wrote it if someone was going to get me on that one  .

BTW the rectifier was not the problem or a problem. I should be getting my adjustable resistor any day now.

[BruceM]

I've been using my own AVR for a couple years and would never go back.  My appliances are much happier (no longer humming and moaning) with the better looking sine wave when not using the harmonic winding for excitation.

I do have a dropping resistor for my harmonic excitation (it's there as a backup system).  That does work well for adjusting the voltage.

Bruce M

[NoSpark]

It takes almost all of the 10 ohms of the adjustable resistor to get my st5 down to 120v. If I load one leg hard the other goes up 10v from 120v so the loaded leg may be 115v while the unloaded leg is 130v . Maybe I should have got a 15 or 20 ohm resistor  .  I suppose this could all change with the 60' run to the main breaker panel in the basement.

[BruceM]

I had my harmonic dropping resistor just perfect, then I added some 0.1uF caps around the bridge and the voltage raised- just past the maximum of my adjustable resistor.  Grrr. 

I just ignore it as the AVR kicks in after a second.